Compensating system



June 19, 1934. c. F. WAGNER 1,963,182

COMPENSATING SYSTEM Filed Marchi, 1955 l s sheets-sheet l Power SQL/rca 'x x/ me wxTNEssEs: NvENToR V20/Zes /A/gmer.

ATTGRN EY June 19,1934. c. F. WAGNER COMPENSATING SYSTEM Filed March l, 1955 3 Sheets-Sheet 2 fig-6.

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307m@ FI June 19, 1934. Q F, WAGNER 1,963,182

COMPENSATING SYSTEM Filed March4 l, 1935 5 Sheets-Sheet f5 .S Saz/Iv ZIP/0% e wnnssses: e xNvENToR v Y Charles/7 Wagner'.

' rE'brl'Eg- @j .l @l l BY ATQN EY Patented June i9,l 1934 1,903,132 couranss'rmc sYs'rEM Char-ie. r. warner, summers., winmt Westinghouse Electric Manufacturing Company, East Pittsburgh, Pa... a corporation of Pennsylvania application mmh 1, Awas, seria No. 659,119

' 1o claims. (Cl. 1v1-11s) My'invention relates to compensating means for automatic regulators and has particular relation to line-drop compensators employed with voltage regulators connected in open delta relation in three-phase power ton and distribution circuits.

Because automatic feeder voltage regulators are usually located at some distance from the point of power distribution at which it is desired l0 that the voltage be maintained constant, it is necessary to provide means for compensating the control of the regulators in accordance with the voltage drop in the feeder circuit. This voltage drop varies in accordancewith the current flowing in the circuit and is the vector sum of the resistance and reactance components of voltage drop in the circuit impedance. To eilfect such compensation, a device known as a line-drop compensator is employed in the control circuit of each regulator operating means.

Such a line drop compensator is in eiiect a duplication in miniature of the line from the regulator to the point of Aload distribution. Through it a current is passed that is proportional to the line current and which causes a voltage drop across it that is proportional to the line drop in voltage. From a measure of this voltage drop,

the regulator adjusts itself to maintain the proper voltage at the distant distribution center.

In the application of induction or other voltage regulators to three phase, three-wire circuits, only two single-phase regulators per circuit need be utilized, they being connected in well known manner in an open delta connection. In such a three-phase system the line current is at unity power factor out of phase with the line-toline voltage. Consequently, there is a 30 phase displacement 'between the readily available voltage and current quantities which may be utilized to respectively control each regulator and to energize the line-drop compensator therefor.

In the past, it has been deemed necessary to employ special means for bringing the compensator energizing current at unity power factor of the regulated circuit in phase with the circuit voltage which is impressed upon the-regulator control circuit, to eilect. proper operation of the compensating system. One well known practice for attaining this result is to insert a third current transformer in the,common phase conductor of the open delta regulator connection which, when interconnected with the current transformers in the other phase conductors, provides currents havingthe proper phase relation with 55 yrespect to the available line-to-line voltages.

More recently, to eliminate the third current transformer in the common lead, an auxiliary device known as a compensator phase angle transformer has been utilized. Both of these schemes are. however, expensive, the rst because it in- 00 volves not only the cost of the extra current transformer but also its installation which sometimes requires additional structures, and the second because .it entails the expense of a special piece of equipment and necessitates control circuit inter- 66 connections between the two regulators.l

My invention is directed to an improved compensating system, especially adapted for use in connection with open-delta-connected regulators of the type under consideration, which eliminates 70 the disadvantages above named and which possesses additional advantages to be particularized hereinafter.

One object of my invention is to provide a linedrop compensating system for automatic voltage 76 regulators connected in open delta in three phase circuits that is simple in construction, inexpensive to build, and that requires a minimum amount of equipment.

A further object of myv invention is to provide so means whereby a line drop compensator utilized with a voltage regulator may be directly energized by a current which bears a predetermined phase displacement with respect to the circuit voltage' impressed upon the regulator control circuit.

Another object of my invention is to provide a compensating system for open delta connected regulators which requires no control circuit interconnections between the two single phase regulators utilized.

I have discovered that in the case of an autolmatic voltage regulator application, rwhere the line current readily available for compensator energization isdisplaced, at unity power factor, by 30 from the line-to-line voltage from which the 95 regulator operating means derive control, if the resistance and reactance elements of Ythe compensator are properly adjusted not as in accordance with the prior practice to be proportional, respectively, to the resistance and reactance components oi line impedance but in a special manner to be more completely described, the operation of the compensator will be exactly the same as were an in-phase energizing current to be utilized with the settings of the compensator elements proportional to the line components of impedance. Hence, by setting the compensator in accordance with the teachings of my invention, the special phase shifting equipment and the interconnection of the regulator control no los circuits heretofore required in open delta applications may be entirely dispensed with, thereby allowing marked savings in the cost of the compensating equipment and corresponding advances in the simplicity thereof to at once be effected.

My invention will be best understood through the following description of specific embodiments thereof when taken in conjunction with the accompanying drawings, in which:

Figure 1 is a diagrammatic View of apparatus and circuits illustrating the simplified compensating system of my invention applied to each of two single phase automatic voltage regulators disposed in open delta relation in a threephase transmission circuit,

Fig, 2 is a diagram of vectors illustrating the phase angle relation, at unity power factor, of the voltages and currents acting in the several phases of the transmission circuit shown in Fig. 1, l

Fig. 3 is a Vector diagram illustrating the effective voltage drops, at unity power factor, through the impedance of the transmission line which must be compensated for in controlling each of the regulators of Fig. l,

Fig. 4 is a Vector diagram illustrating the manner in which special settings of the resistance and reactance elements of the compensators of Fig. l permit these simplified compensating devices to satisfactorily function when energized by currents displaced, at unity power factor, by 30 from the voltages impressed upon the regulator control circuit,

Fig. 5 is a vector diagram showing that when the compensator energizing current lags the voltage by 30 the special settings of the compensator elements provided by my invention are such that the phase angle of the compensator impedance is 30 greater than the phase angle of the compensated line or transmission circuit impedance,

Fig. 6 is a vector diagram similarly illustrating the proper settings of the compensator energized by a current which leads the voltage by 30 as those in which the compensator phase angle is 30 less than the angle of the line impedance,

Figs. 'Z and 8 are vector diagrams showing the current and voltage relations in the three phase transmission circuit for lagging and leading power factor loads thereof respectively and illustrating that changes in power factor have no effect upon the special settings of the compensator elements,

Figs. 9 and 10 are vector diagrams showing that when the phase angle of the impedance of the line to be compensated lies outside of a given range of values the compensator adjusted in accordance with my invention must supply negative values of resistance and reactance respectively,

Fig. 11 is a diagrammatic view of apparatus and circuits illustrating means for enabling a simplified compensator of the type illustrated in Fig. 1 to supply either positive or negative values of resistance and reactance,

Fig. 12 is a similar representation of component reversing means applied to a compensator of a well known rotary contactless type.

Fig. 13 is a diagrammatic representation of apparatus and circuits illustrating a special interconnection of the two current transformers which energize the compensators of the two regulators disposed in open delta which causes the energizing current of both compensators to lead, at unity Ulla...

power factor, the associated line-to-line voltage by 30,

Fig. 14 is a vector diagram illustrating the manner in which this leading current is supplied to the compensator associated with the line in which the main circuit current lags the line-toline voltage by 30,

Fig. l5 is a diagrammatic represenation of apparatus and circuits illustrating an interconnection of the two current transformers which causes the energizing current of both compensators to lag, at unity power factor, the corresponding line-to-line voltage in the three-phase circuit by 30, and

Fig- 16 is a vector diagram illustrating the manner in which the lagging current is supplied to the compensator associated with the line in which the main power current leads the associated line-to-line voltage by 30.

Referring to the drawings and particularly to Fig. 1 thereof I have there illustrated two voltage regulators 10.and 12 of a well known induction type connected/in open delta relation in a threephase transmission circuit which comprises line conductors A, B and C, shown as terminating at a point distant from the regulators. The two regulators 10 and 12 respectively comprise series windings 14 and l5 connected to introduce corrective voltages into transmission circuit conductors A and B, respectively, to thereby modify the circuit supply source potentials, and exciting windings 16 and 17 energized by the voltages acting between the common line conductor of the open delta regulator connection and the two outer line conductors with which the two regulators l0 and 12 are respectively associated. It will be understood that in a regulator of this type, the magnitude and direction of the corrective voltage introduced by the series winding is controlled by varying the inductive relation of the series and exciting windings, such as by mechanically moving or rotating the plane of one winding with respect to the plane of the other.

As shown, regulators 10 and 12 are respectively operated by means of reversible motors 20 and 22 mechanically connected thereto through suitable gearing. The motors 20 and 22 are similar, each comprising an armature winding 23 and differentially related series field windings 24 and 25. When energized from a suitable source of power as, for example, a battery 27, through winding 25, the motors 20 and 22 are caused to rotate in the voltage-raising direction and when energized through winding 24 the motors rotate in the voltage-lowering direction.

To control the operation of the regulator motors 20 and 22, in accordance with changes in the voltage of the regulated circuit, contact making voltmeters or primary relays 28 and 30 are provided. 'I'he primary relay 28, to which the relay 30 is similar, comprises fixed contact members 31 and 32 disposed in engageable relation with a movable contact member 33, the position of which is controlled by the magnitude of the voltage which energizes an operating winding 35 of the relay.

When the voltage impressed upon the winding 35 of the primary relay 28 rises above a predetermined value the contact member 33 will be moved into engagement with the contact member 31 to complete an energizing circuit for the regulator motor 20 causing it to actuate the regulator in the voltage-lowering direction. Similarly, when the voltage impressed upon the relay winding drops below a predetermined value, engagement of contact members 33 and 32 is effected to operate motor 20 in the voltage-raising direct/ion.

It will thus be seen that the regulator 10 will be operated to maintain at a constant value the voltage which energizes its primary relay 28. In a similar manner, the regulator 12 will also be operated to maintain at a constant value the voltage which energizes its primary relay 30.

Voltages for controlling the primary relays 28 and 30 are respectively supplied through potential transformers 38 and 39 which are respectively energized in the manner shown by potentials En. and EN appearing between the lines of the transmission circuit at the location of the regulators. To compensate the voltage drop which occurs in the transmission circuit between points K and D, which impedance is schematically represented as a resistor R and an inductor X in each of the circuit lines, the voltage-modifying or compensating equipments 40 and 41 are utilized in association with the primary relay energizing circuits.

Equipment 40 comprises a` resistor element 43 and an inductor element 44 connected intermediate potential transformer 38 and the primary relay 2.8. Through a portion of each of elements 43 and 44, adjustable by means of tap connections 60 and 61 associated therewith, is circulated, from a current transformer 46, a current which is proportional to the current Is flowing inthe circuit conductor A. In a similar mannenequipment 41 comprises-a resistor element 47 and an inductor element 48 through which a current transformer 49 circulates a current proportional to the current L flowingin transmission circuit conductor C.

As illustrated by the vector diagram of Fig. 2, in which voltages Es. Eb andv Ee represent the equivalent star or Y connection voltages impressed by a supply source (not shown) upon the conductors or lines A, B and C of the transmission circuit and Il, Ib and In the currents flowing in conductors A, B and C at a given value of unity power factor load. The line-to-line voltage'Eb. which energizes transformer 38 has such a phase position that assuming a phase rotation of A-B-C, current I. lags it by 30 and line-to-line voltage Esc which energizes the transformer 39 has such a phase position that current Ie leads it by 30.

'I'he vector diagram of Fig. 3 illustrates, when the circuit conditions are as given by the diagram of Fig. 2, the voltage drops which occur in that portion of the line between the regulators, or point K, and a distant center of distribution, designated by D, at which it is desired that the regulators maintain constant the circuit voltage.

This circuit voltage to be held constant is designated at E'bs for the value appearing between lines A and B and Ebc for the value appearing between lines B and C. It will be noted that the resistance component of line drop RI and reactance component XI combine to form the total impedance drop Erd which vectorially combines with Eb to produce Ess and with E'se to produce Esc.

In order that the regulators 10 and 12 may function to maintain constant the circuit voltage at the center of distribution D, it is necessary that primary relay 28 be influenced by a voltage equivalent to Eb.. and that relay 30 similarly be influenced by a voltage equivalent to E'bc. In the past, this desired result has been attained by energizing each compensator by a current which at unity power factor is in phase with the voltage acting in the primary relay circuit. In other words past practice has been to set the resistance and reactance elements of the compensator so that the voltage drops through them set up bythe compensator energizing current will be respectively proportional andv equivalent to the voltage drops which occur in the circuit or line to be compensated due to the resistance and reactance components of the line impedance. The auxiliary equipmentn, as already explained, to provide the desired in-phase relation, in an open delta installation of two single phase regulators with a three phase on circuit, has materially increased the expense and complication of the complete compensating equipment.

In order to eliminate this added expense and complication, I utilize, as before mentioned, the 30 displaced line current directly available at cach regulator to energize the compensator and I so modify the settings of the resistance and reactance elements thereof that the error intro` duced by the displaced current is corrected, thereby allowing the compensation to be an exact equivalent of that attainable in the prior art inphase energization system explained.

To more fully explain the special expedients of my invention, the vector diagrams of Figs. 4, 5 and 6 may be referred to. In the diagram of Fig. 4 which is a substantial reproduction of Fig. 3, it will be seen that the line impedance'drop vector Em instead of being made up of the two components RIand XI of Fig. 3, may in the case of the compensator associated with'regulator 10 in transmission line A be made up of a modified vector riIs which is in phase with line current L and a modified vector :1L displaced 90 therefrom. That is, for the situation in which the energizing current Is of the compensator 40 of Fig. 1 lags the associated line-to-line voltage Em by 30, it is only necessary to reduce the setting of resistor element 43 and increase the setting of reactance element 44 to obtain the same results as are obtainable through the usual n-phase current energization of the compensator.

Likewise, in the case of compensator 41 associated with the regulator 12 in transmission line C, vthe desired impedance drop Em may be obtained when the compensator is energized by line current Ic which leads the associated line-to-line voltage Esc by 30 by changing the setting of resistance element 47 to provide a modified vector rzIc in phase with the line current and reducing the setting of reactance element 48 to provide a modified vector 2:21a. A

In arriving at the proper values of these modifled compensator element settings, the settings in accordance with the prior art method, in which the compensator is energized by a current which is in phase with the primary relay circuit energizing voltage at unity power factor of the regulated circuit load, are first determined. In accordance with this prior art method, the com'- pensator is set for an impedance having a magnitude equivalent to the value of impedance in the line to be compensated for and an angle equal to the angle 'of that line impedance. In other words, the settings of the' resistance and reactance elements are so made that the voltage drops through them will be respectively propory of this invention in which the compensator is energized by a current which at unity power factor is displaced 30"` from the primary relay circuit energizing voltage, in the following manner:

For the ease in which the current lags the voltage by 30, typified by compensator 40 in the showing of Fig. 1, the compensator is set for an impedance having a magnitude equivalent to the value of the line impedance and having an angle 30 greater than the angle of the line impedance. Such a setting may be obtained as reterence to Fig. 5 will presently indicate, by multiplying the setting that would be made were the compensator energizing current in phase with the voltage at unity power factor by (0.866+j0.5). Thus above expressions i is the well known complex quantity factor applicable to vector analysis, r1 and im are respectively the proper settings for the resistance and reactance elements of the compensator for the 30 lagging current, and R and 9X are the usual settings of the elements, when the compensator is energized by an in-phase current at unity power factor.

This relation is more clearly depicted by the vector diagram of Fig. 5, in which angle L; represents the phase angle of the line impedance for the particular values of resistance and reactance components assumed in the vector diagrams of Figs. 3 and 4. The proper setting of the elements of the compensator 40, when energized by the lagging current Ia, is such that its phase angle In the will be Lvl-30 or Gi.

For the case in which the compensator energizing current leads the voltage by 30, which is typified by compensator 41 in the system of Fig. 1, the compensator should be set for an impedance having a magnitude equivalent to the value of line impedance and having an angle 30 less than the value of the line impedance. Such a setting may be obtained by multiplying the setting that would be made were the compensator energizing current in phase with the voltage at unity power factor by (0866-705) Thus,

In the above expression, rz and ix: are, respectively, the proper settings of the resistance and reactance elements of the compensator when its energizing current leads the voltage by 30 and R and iX are the usual settings of the compensator when it is energized by an in-phase current.

The above relation is vectorially depicted by the diagram of Fig 6, in which the special settings of the compensator energized by the 30 leading current Ic 'are such that the phase angle G2 of its impedance has a value 30 less than that of the line impedance angle L1.

That these special settings are satisfactory for changing values of regulated circuit power factor will be apparent from an inspection of the vector diagrams of Figs. 1 .and 8, which are drawn to illustrate conditions of lagging and leading load currents, respectively. In Fig. '1, for example, in which currents I., In and L are shown as lagging the corresponding phase voltages by an angle alpha, the compensator impedance triangles, which cause the regulators to boost the circuit supply of voltages by values suiicient to compensate for the line drop, are rotated through a corresponding angie, thereby accounting for the greater illustrated dinerence between voltages E's; and Eb. controlled by regulator 10 in the system of Fig. 1, and voltages E and Esc controlled by regulator 12.

Likewise, in the case of a leading power factor load shown in Fig. 8, by a similar displacement in the leading direction of the line currents In, Ib, and In, the compensator impedance triangles are correspondingly rotated in the opposite direction to cause the regulators to reduce the supply voltages Es. and Ete to values necessary to maintain constant the voltages Esa and Ebc at the distant center of distribution. Hence, while the original discussion has assumed unity power factor, it will be seen that the conclusions may be extended to any power factor as the system still permits the compensating voltage that is introduced in the relay circuit to appropriately vary with the power factor.

Since the system requires that the phase angle of the compensator impedance be rotated 30 with respect to the impedance angle of the line to be compensated, negative resistances may be encountered in increasing the phase angle when the regulator is connected to open-air lines typiiied by the vector diagram of Fig. 9, and negative reactances may be encountered in decreasing the phase angle when the regulator is connected to cable circuits typified by the vector diagram of Fig. 10.

Fig. 9 represents a line or circuit having a large value of reactance X as compared with its resistance R', thereby producing a line impedance phase angle Lz, which is in excess of 60. For this condition, the proper angle for the setting of a compensator energized by a 30 lagging current 110 is L2+30 or Go. Since G3 is in excess of 90, the resistance component nl; must be negative, as illustrated, the reactance component :1:31a remaining positive as before.

Similarly, when the line to be compensated possesses such a low value of reactance X" as compared with its resistance R" that the imped ance La is less than 30, as shown in Fig. 10, an energization of the compensator by a 30 leading current Ic necessitates that the reactance component :Je of the compensator impedance be negative, in order that the angle of the compensator G4 may be of the proper value required for this condition. The resistance component 141e of the compensator impedance is positive as be- 125 ore.

The explained conditions in which negative values of compensator resistance and reactance are required necessitate that the compensator devices utilized in the system of my invention be capable of providing these negative values in addition to the usual positive values. A compensator possessing this characteristic is disclosed and claimed in a copending application Serial No. 659,163, by E. R, Wolfert, filed March 1, 1933, and assigned to the same assignee as this invention. The compensator there described is inherently capable ot providing both negative and positive values of resistance and reactance.

However, when no such improved device is available, compensators capable only of positive values may be modied in accordance with the showingsofFigs. 11 andl2tofulillltheabove stated requirement. In Fig. 11, the simplified compensatorshownat 40inthesystemoi'Fig-1 145 is illustrated. Intermediate the resistance and reactance elements 43 and 44 of this compensator and the energizing circuit for winding 35 of primary relay 28 are reversing switches 56and58. Whenthebladesofthesetwoswitches 150 voltage drop across this element to act negatively in the relay circuit, as is required for the condi- `'tions deplctedin Fig. 9. Similarly, a movement of the blades of switch 58 to the downward position effects a reversal of the connections of .reactance element 44, thereby supplying the negative value of the reactance component required when the circuit conditions are as depicted by Fig. lp.

Fig. 12 illustrates a compensator known in the art as the rotary contactless type in which the reversing switch is applied. Instead of providing the resistance and reactance elements thereof with tap connections, shown at 60 and 61 for the compensator 40 of Figs. 1 and 11. the device of Fig. 12 utilizes two variometer assemblies 63 and 64, each of which comprises a plurality of inductiveLv adjustable windings more completely described in U. S. Patent No. 1,858,845, issued to E. R. Wolfert May 1'1. 1932, and assigned to the same assignee as this invention. With this particular compensator, the reversing switches 56 and 58 perform exactly` the same function as in the case of compensator 40 ofFig. 11.

The compensating system thus far described involves no control circuit 'connections between the two regulators disposed in delta relation in the three-phase transmission circuit, but, in certain cases, may require, as has been seen, a compensator element reversing switch. Additional schemes involving no reversing devices, but requiring control-circuit connections between the regulators, are shown in Figs. 13 and 15. 'Ihese two systems possess a further advantage in that a similar setting of the compensators for both regulators may be made. 'I'he three-phase power circuit and the regulators 10 and 12, with which they are illustrated, will be seen to be an exact reproduction of the showing of Fig. 1.

The system of Fig. 13 is especially useful when it is known that the line or circuit to be cornpensated possesses characteristics giving it an impedance angle which is greater than 60. By interconnecting the two' current transformers 46 and 49 in the manner shown, both compensators 40 and 4l may be supplied by a current which leads the associated line-to-line voltage by 30 at unity power factor of the regulated circuit load. This relation is illustrated by the vector diagram of Fig. 14.

Compensator 41 is energized, as in Fig. i, directly by the current Ic supplied through current transformer 49. This current leads by 30 the voltage Esc, which energizes the actuating winding of primary relay 30. Compensator 40, however, is, by virtue of the interconnections 66 and 67 between the two current transformers, energized by the vector sum of currents Is and Ic,

Vwhich combined current, equivalent to Is, is reversed before being impressed upon the compensator in order that it may lead the voltage Esa, which energizes the. energizing winding of relay 28, by 30". 'I'his reversed current is indicated in ,the diagram by vector-(Ia-i-Ie) As a result of this similarity in phase position and magnitude of the two compensator energizing currents, compensator 40 may be set in exactly the same manner as is compensator 4l, which manner has already been explained in detail. In

particular interconnection of current transformers is especially useful when it is known that the f impedance angle of the line to be compensated is.- less than 30. By virtue of interconnections'66'f' -asso'ciated line-to-line voltages` by 30.. This` and 67' between the current transformers 46. and

49, compensator 41 is supplied with the sum ofi currents Irl-Is reversed, as indicated at-(L+I) l in the vector diagram of Fig. 16, compensator 40'- being energized in the usual manner directly' by the current I. through current transformer 4'6.

It will be apparent that both of the campen-V sators may now be set` for a phase angle 30` greater than the impedance' angle of the line,'and, further, that the need for negative values of re'-`l sistance and reactance is, under the conditions named, effectively eliminated. In all of the foregoing analysis, a phase rotationA-B-Chasbeenassumed. "':l Although I have shown and described certain? specic embodiments of my` invention, I am fully z aware that many modifications thereof are pos'- sible. My invention, therefore, is not to be rc-` stricted except insofar as necessitated by the priorz art and by the scope of the appended claims; 1,- -r I claim as my invention: f- 1. In combination, an alternatin -curle'ntpower circuit in which the line current, at unity* power factor, is displaced a given angle from the.:` line-to-line voltage of the circuit, a regulator dis@ a' posed to control the voltage `of said circuit, a primary relay for controlling the operation'of saici regulator, a circuit for energizing said relay bya measure of the said line-to-lne voltage, aline' drop compensator comprising a resistance ele-5 ment and a reactance element disposed in saidf relay energizing circuit, and means for energia-'f' ing said compensator by a measure of` thesaid' power-circuit line current, the elements 'of the compensator being so adjusted that the compeii'- i:

sator impedance has a phase angle diifer'ing fr'oiii'- that of the power circuit impedance by the said:

at unity power factor.

2. In combinationya voltage Vregulator dise, posed in an alternating-current power circuit iii-f which the line current, at unity power factoi-,is displaced a given angle from the line-to-line? voltage, said regulator having an operation-Q control relay and an operating circuit thereforh that is supplied with a voltage that varies in" accordance with the said line-to-line voltage, a circuit-impedance drop compensator, j energized D by the said line current, comprising x'i.resistia.n ceelement and a reactance elementl disposed in said relay energizing circuit, the elements of .tiief compensator being so set that they present impedance equivalent to that of the power cir cuit the voltage drop through which is to be compensated and having a phase angle differing from that of the said power circuit impedance by the said given angle of displacement at unity'l power factor of the power-circuit line current'v with respect to the power-circuit line-to-line f voltage.

connected in open-delta relation in a threephase power-transmission circuit, each of said regulators having an operation-control relay with an energizing circuit therefor which is supplied by a measure of the associated line-toline voltage of the circuit, a line-drop compensator comprising a resistance element and a reactance element disposed in the energizing circuit of each of said relays, and means for energizing one of said compensators by a measure of the power-circuit line current which, at unity power factor, lags the line-to-line voltage supplying the associated relay by 30, the elements of the compensator being so adjusted that the compensator impedance has a phase angle which is 30 greater than that of the power circuit impedance the voltage drop through which is to be simulated by the compensator.

4. In combination, a pair of voltage regulators connected in open-delta relation in a threephase power-transmission circuit, each of said regulators having an operation-control relay and an energizing circuit therefor that is supplied with a voltage that varies in accordance with the associated line-to-line voltage of the circuit, a line-drop compensator comprising a resistance element and a reactance element disposed in the energizing circuit of each of said relays, and means ior energizing one of said compensators by a measure of the power-circuit line current which, at unity power factor, leads the line-to-line voltage supplying the associated relay by 30, the elements of the compensator being so dimensioned that the compensator impedance has a phase angle which is 30 less than that of the power circuit impedance the voltage drop through which is to be simulated by the compensator.

5. In a system comprising two voltage regulators connected in open-delta relation in a three-phase power-transmission circuit, each of said regulators having an operation-control relay and an energizing circuit therefor that is supplied in accordance with the associated lineto-line voltage of the power circuit, the combination with each regulator, of a circuit-impedance-drop compensator, energized by a measure of the current flowing in the regulatorconnected line of the power circuit, comprising a resistance element and a reactance element disposed in the said energizing circuit for the relay of that regulator, the elements of the compensator whose energizing current lags, at unity power factor, the associated relay supply voltage by 30 being so adjusted that the compensator impedance has a phase angle which is 30 greater than the angle of the power-circuit impedance the voltage drop through which is to be simulated in the relay-energizing circuit by the compensator.

6. In a system comprising two voltage regulators connected in open-delta relation in a threephase power-transmission circuit, each of said regulators having an operation-control relay and an energizing circuit therefor that is supplied in accordance with the associated line-toline voltage of the power circuit, the combination, with each regulator, of a circuit-impedance-drop compensator, energized by a measure of the current flowing in the regulator-connected line of the power circuit, comprising a resistance element and a reactance element disposed in the said energizing circuit for the relay of that regulator, the elements of the compensator whose energizing current leads, at unity power factor, the associated relay supply voltage by 30 being so set that the compensator impedance has a phase angle which is 30 less than the angle of the power-circuit impedance the voltage drop through which is to be simulated in the relay-energizing circuit by the compensator.

'7. In a system comprising two voltage regulators connected in open-delta relation in a threephase power-transmission circuit, each of said regulators having an operation-control relay and an energizing circuit therefor that is supplied in accordance with the associated line-to-line voltage of the power circuit, the combination, of a circuit-impedance drop compensator for each regulatorvenergized by a measure of the current flowing in the regulator-connected line of the power circuit, comprising a resistance element and a reactance element disposed in the said energizing circuit for the relay of that regulator, the elements of the compensator whose energizing current lags, at unity power factor, the associated relay supply voltage by 30 being so set that the compensator impedance has a phase angle which is 30 greater than, and the elements of the compensator whose energizing current leads, at unity power factor, the associated relay supply voltage by 30 being so set that the compensator impedance has a phase angle which is 30 less than the angle of that portion of power circuit impedance the voltage drop through which is to be corrected by the compensators.

8. In a system comprising two voltage regulators connected in open-delta relation in a threephase power-transmission circuit, each of said regulators having an operation-control relay and an energizing circuit therefor that is supplied in accordance with the associated line-to-line voltage of the power circuit, the combination, with each regulator, of a line-drop compensator, energized by a measure of the current flowing in the regulator-connected line of the power circuit, disposed in the said energizing circuit for the relay of that regulator, the compensator whose energizing current lags, at unity power factor, the associated relay supply voltage by 30 being so set that its impedance has a phase angle which is 30 greater, and the compensator whose energizing current leads, at unity power factor, the associated relay supply voltage by 30 being so set that its impedance has a phase angle which is 30 less, than the angle of that portion of power circuit impedance the voltage drop through which is to be corrected by the compensators, the magnitude of each compensator impedance being equivalent to the impedance of the said portion of the power circuit.

9. In a regulating system comprising two voltage-adjusting means connected in open-delta relation in a three-phase power-transmission circuit, each of said adjusting means having an operation-control relay and an energizing circuit therefor that is supplied with a voltage that varies in accordance with the associated line-toline voltage of the power circuit, and a line-drop compensator disposed in each relay-energizing circuit, the combination of compensator-energizing means comprising a current transformer in each of the power-circuit lines in which the said voltage-adjusting means are connected, the

compensator associated with the line in which,

at unity power factor, the power current lags by 30 the associated line-to-line voltage being energized by the current supplied through the current transformer in that line. and the compensator associated with the other line in which.

at unity power factor, the power current leads by 30 the associated line-to-line voltage, being energized by the reversed sum of the currents supplied through both of said current transformers, said summation current reversed thus also lagging by 30 the compensator-associated line-to-line voltage of the power circuit.

` 10. In a regulating system comprising two voltage-adjusting means disposed in open-delta relation in a three-phase power-transmission circuit, each of said adjusting means having an operation-control relay and an energizing circuit therefor that is supplied from the associated line-to-line voltage of the power circuit, and a line-drop compensator disposed in each relayenergizing circuit, the combination of compensator-energizing means comprising a current transformer in each of the power-circuit lines in which the said voltage-adjusting means are connected, the compensator associated with the4 CHARLES F. WAGNER. 

